A VIBRATION DAMPER FOR A CHIMNEY

Abstract: A vibration damper for a chimney comprising a partly liquid-filled container which is positioned at the top of the chimney and in which a plurality of perforated plate members are secured, said plate members extending from the bottom of the container and upwardly in a manner such that the plate members divide the container into separate spaces which are in mutual flow communication via the perforations of the plate members, and which additionally comprises at least one substantially horizontal perforated plate member at the surface of the liquid. The resulting vibration damper, which has an inexpensive, relatively maintenance-free structure, has improved damping properties over the prior art.

Description: A vibration damper for a chimney The present invention concerns a vibration damper for chimneys, comprising a partly liquid-filled container, which is placed at the top of the chimney and in which a plurality of perforated plate members are secured, said plate members extending from below and upwardly in a manner such that the plate members divide the container into spaces which are in mutual flow communication via the perforations of the plate members. Tall chimneys, in particular free-standing chimneys fre¬ quently involve the problem that the passage of the wind around the chimney, e.g. in case of a circular chimney, causes a variable pressure field which subjects the chim¬ ney to forces at right angles to the wind direction. At special wind velocities this may cause a resonance load which may lead to extremely violent transverse oscilla¬ tions of the chimney. In addition to being unpleasant because they can i.a. initiate noise by the shakings, such transverse oscillations can also be dangerous to the chimney, since they can cause fatique failure in the structure of the chimney, and, in extreme cases, can cause the chimney to tumble down. Therefore, in particular in connection with very thin chimneys, the top of the chimney is frequently equipped with a vibration damper which, so to speak, drains the chimney of the energy supplied through the wind and con- verts it into thermal energy which is released to the sur¬ roundings. Through the years, numerous vibration dampers have been proposed for this purpose, some of which are based on the fundamental principle of suspending a solid mass fric- tionally and resiliently movably with respect to the structure of the chimney, so that this mass will serve as a vibration damper. Such structures are relatively expen¬ sive and frequently require maintenance in order to main- tain the desired damping characteristics, since the movable frictional elements may change e.g. the damping characteristecs due to tear and wear, weather conditions and the like. In contrast, the German Auslegeschrift 1227633 proposes a vibration damper for a chimney which is based on the prin¬ ciple mentioned in the opening paragraph, the top of said chimney being provided with a container in which a plura¬ lity of vertical, perforated plate members are secured so as to divide the container into separate spaces which are in mutual flow communication via the perforations of the plate members. Since the container is partly filled with a liquid, the vibration damper operates in that the liquid, when the chimney is set into vibrations, try to flow through the perforations on the plate members immersed in the liquid, so that the created turbulence in the water as well as the internal friction causes energy in the form of heat to be dissipated to the structure and further on to the surroundings. Thus, there is provided a vibration damper for a chimney which is relatively mainte¬ nance-free, since the vibration damper operates quite without any mechanical guides, springs, dampers, etc. The present invention is based on this fundamental prin- ciple according to the German Auslegeschrift 1227633 and is thus a further development of this. The object of the present invention is to provide a vibra¬ tion damper which is simple and inexpensive to manufac- ture, and which exhibits improved properties with respect to damping, in particular when vibrations are initiated. This is obtained in that the vibration damper is con¬ structed as stated in claim 1, since the liquid amount contained in the container, by means of e.g. a substan¬ tially horizontal perforated plate member at the surface of the liquid, is prevented from moving freely upwards in the container, as is the case according to the German Aus¬ legeschrift 1227633. In contrast, the transverse vibration movement of the chimney causes the liquid contained in the container to flow through perforations in the horizontal plate as well as in the perforated plate members which extend from the bottom of the container and upwards. This results in a good damping with a relatively small consumptions of the perforated plates, since the horizontal plate primarily dampens the large vertical movements at the surface, and the perforated plates, which extend from the bottom of the container and upwards, dampen horizontal flows in the liquid. In this connection the German Auslegeschrift 1275759 teaches equipping vibration dampers for the chimneys with horizontal plates which are immersed in a liquid in the damper container. Here a plurality of plates are used, preferably concentrated at the bottom of the container, thereby providing damping by friction caused by the horizontal flow of the liquid through the plates. For this liquid flow to take place at all, the plates are provided with holes, so that the liquid can escape upwards. In practice, this means that the damping effect increases with the size of the holes in the horizontal plates, since, other things being equal, the liquid will flow more rapidly. Therefore, the holes in the plates are provided with a quite different purpose and with a quite different effect than the perforations in the horizontal plates according to the present invention. The vibration damper of the invention may comprise a plu¬ rality of horizontal perforated plate members at the sur¬ face of the liquid, but in an expedient embodiment just one horizontal perforated plate is used at the surface of the liquid, since expedient dimensioning of the number of perforations in the plate as well as the area of the per¬ foration can provide approximately the same damping cha¬ racteristics as when several plates are used. When the horizontal perforated plate is located in or below the surface of the liquid, as stated in claim 3, a particularly good damping is obtained, since the liquid present below the plate is protected completely against free vertical movments, apart from flow through the per- forations in the plate. When the plates extending from the bottom of the container extend entirely below the horizontal plate, as is stated in claim 4, the total area of the perforated plates is utilized optimally, while obtaining a significant advan¬ tage in terms of manufacture, since the plates can be secured to each other in a simple manner and thus have a stiffening effect on each other. Claims 5 and 6 define embodiments of the invention which are particularly expe- dient in terms of manufacture, and which provide good damping properties in relation to the consumption of material for the overall structure. The invention will be desribed more fully below with refe- rence to the drawing, in which: fig. 1 is a side view of a chimney having a vibration damper positioned at the top of the chimney, fig. 2 is a top view in horizontal section through a vibration damper according to the invention, fig. 3 is a lateral view of a fragment of a vibration damper, and fig. 4 shows a vibration damper like in fig. 3, but in an alternative embodiment. Fig. 1 shows a chimney 1 of a free-standing type, i.e. it is supported only by the foundation 3 which keeps the chimney upright. The chimney is equipped with a flue gas inlet opening 4 and an outlet opening or top 2. The shown chimney is made of steel plates having a circular cross- section. A vibration damper 5 according to the invention is provided in a known manner at the top 2 of the chimney, and this vibration damper 5 may either be mounted directly on the chimney as an integral unit, or it may be formed by an independent unit which can subsequently be mounted on e.g. existing chimneys which are already in use. The main point is that the vibration damper 5 is connected rela¬ tively stiffly with the structure of the chimney 1, so that vibrations in the chimney, possibly caused by the wind, are transferred directly to the vibration damper. In principle, the vibration damper 5 may be positioned anywhere on the chimney 1, but it is clear that the damp- ing effect is achieved best when the vibration damper 5 is positioned on the chimney 1 at the place where the vibra¬ tion amplitude of the chimney 1 is greatest. That is at the top 2 of the chimney 1. Fig. 2 is a sectional top view of the vibration damper 5 of fig. 1. As will be seen, the outer wall 6 and the inner wall 7 define a container which accommodates a horizontal circular plate 8 having perforations, with radially ex¬ tending, vertical, perforated plates 9a, 9b, 9c positioned along the entire circumference. As will be seen from fig. 3, the container of the vibra¬ tion damper is upwardly defined by a plate 10 and down¬ wardly by a corresponding plate 11. The vertical, radially extending plates 9a, 9b, 9c extend, as will be seen in the figure, from the base plate 11 of the container up to the horizontal perforated damping plate 8, and, as will be seen in the figure, the container is partly filled with a liquid, the liquid level being indicated by 12. It will be seen that both the vertical damping plates 9a, 9b, 9c and the horizontal damping plate 8 are totally immersed in the liquid when the liquid is stationary. In a situation where the container influences a vibration movement from the chimney 1, the liquid contained in the container will consequently begin flowing to and fro in the container. Liquid in the lower part of the container will hereby be forced primarily through the perforations on the vertical plates, and the liquid in the upper part of the container, i.e. at the liquid surface 12, will be forced through the horizontal perforated plate 8. It will clear from the foregoing that while it is possible to ob¬ tain a damping effect using horizontal perforated plates in the lower layer of the liquid and e.g. vertical per¬ forated plates in the upper layer of the liquid, optimum utilization of the area of the damping plates is obtained if the horizontal damping plates 8 are located near the liquid surface 12, and the vertical damping plates 9a, 9b, 9c are located below the horizontal plate 8. As will be seen from fig. 4, it is possible to use several - two being shown - horizontal damping plates 8a, 8b which are positioned relatively close to each other at the liquid surface 12 in accordance with the idea of the invention. In an embodiment (not shown) the vertical damping plates 9a, 9b, 9c may e.g. extend all the way along the bottom 11 of the container to the top 10 of the container. However, it is preferred that these vertical plates 9a, 9b, 9c preferably extend below the horizontal plate 8, since this provides optimum utilization of the area of the plates. While reasonable damping effects can be obtained by positioning the horizontal plates 8 at a small distance above the liquid surface 12, it is preferred that the horizontal plates are slightly immersed in the liquid, as will be seen from figs. 3 and 4, thereby ensuring that the liquid contained or confined between the base plate 11 and the horizontal damping plate 8 is forced to flow through the perforations in the plates rather than performing free lapping movements, as is the case if the horizontal plates 8 are not immersed in the liquid. Depending upon the given chimney structure 1 to be damped, it is clear that the damping properties of the vibration damper 5 must be capable of being adapted to the purpose in question. The structure of the invention provides ample opportunity of varying various parameters with a view to obtaining optimum damping for a given structure. Thus, the number of damper plates, the number of perforations and the area of the perforations in the plates may be varied. Thus, an increase in the number of plates, a reduction in the number of perforations or a reduction in the area of the perforations will cause a greater flow resistance and thereby greater damping, other things being equal. In addition, the overall volume of the container as well as the viscosity of the liquid also influences the damping characteristics of the vibration damper. With a view to ensuring optimum operation of the vibration damper in various weather conditions, it is important i.a. for this reason that the damping liquid contained in the container is an anti-freeze liquid and has a viscosity which is relatively independent of the temperature of the liquid. The embodiment of the invention described above is parti¬ cularly adapted for use in connection with chimneys having a circular cross-section, but it is clear that the basic idea of the invention can be applied to other types of chimneys, e.g. having a rectangular and oval cross-sec¬ tion. In addition, the skilled person has ample opportu¬ nity of using different materials in the structure. Thus, the damping plates may be formed by simple metal plates having punched holes or a lattice plate.

Claims: P a t e n t C l a i m s: 1. A vibration damper for a chimney, comprising a partly liquid filled container which is placed at the top of the chimney and in which a plurality of perforated plate members are secured, said plate members extending from below and upwardly in the container in a manner such that the plate members divide the container into spaces which are in mutual flow communication via the perforations of the plate members, c h a r a c t e r i z e d by addi¬ tionally comprising at least one substantially horizontal, perforated plate member at the surface of the liquid. 2. A vibration damper according to claim 1, c h a r a c ¬ t e r i z e d by comprising just one horizontal, perforated plate at the surface of the liquid. 3. A vibration damper according to claim 2, c h a r a c - t e r i z e d in that the horizontal, perforated plate is positioned in or below the surface of the liquid. 4. A vibration damper according to claim 2 or 3, c h a r a c t e r i z e d in that the perforated plates extending from below and upwardly extend entirely below the horizontal, perforated plate. 5. A vibration damper according to one of the preceding claims, c h a r a c t e r i z e d in that the container is ring-shaped and extends around the chimney. 6. A vibration damper according to claim 5, c h a r a c ¬ t e r i z e d in that the extending perforated plates are approximately vertical and oriented radially with respect to the axis of the container. 7. A vibration damper according to one of the preceding claims, c h a r a c t e r i z e d in that the perforated plates extending from below and upwardly extend right from the bottom of the container.

Inventors: PEDERSEN MICHAEL, PEDERSEN, MICHAEL
Applicants: PEDERSEN MICHAEL, STEELCON CHIMNEY ESBJERG A S, PEDERSEN, MICHAEL, STEELCON CHIMNEY ESBJERG A/S
Application year: 1994
Main classification: E04H12
IPC codes: E04H12